We have observed difference-frequency generation by mixing terahertz and near-infrared laser beams in a crystal (i.e., terahertz frequency upconversion). This process has a potential for detecting terahertz waves. Using an photodiode operating at room temperature the minimum detectable energy per pulse was . When a fast photomultiplier tube was used instead, the lowest-energy per pulse was measured to be . In addition, the temporal profile of the terahertz pulses was measured with a ns resolution.

Subfemtojoule polarization bistable switching in a vertical-cavity surface-emitting laser(VCSEL) is experimentally demonstrated. All-optical flip-flop operation of the VCSEL was performed using two orthogonally polarized injection light pulses. The optimum wavelengths of the two injection pulses for achieving minimum switching power were different and corresponded to the lasing wavelengths of the two polarization states of the laser. The pulse width/switching frequency dependence of the injection pulses showed that a minimum switching energy was obtained at . A record low switching energy of has been achieved as well as a record high switching frequency of .

The application of spectroscopic reflectometry to the monitoring of epitaxial lateral overgrowth of GaN in low pressuremetalorganic vapor phase epitaxy has been investigated. Real-time vertical and lateral growth rates and hence thickness and wing width of the growingGaN are extracted. A vertical growth enhancement was clearly observed at an early stage, followed by vertical growth suppression until full coalescence was achieved. The lateral to vertical growth ratio was obtained showing clear time dependent characteristics. The observations were explained by considering the mass transport between the growing (0001) facets and the sidewall facets.

We have already reported orangish yellow phosphors, and applied them to fabricate warm white light-emitting diodes(LEDs). In this letter, we report on greenish yellow phosphors, and use them to create daylight when coupled to an blue LED chip . The newly discovered phosphors emit at shorter wavelengths of under the excitation, and exhibit a smaller Stokes shift than does. By using this short-wavelength yellow oxynitride phosphor, bright daylight emissions from white LEDs can be generated. Thus, highly efficient white LEDs with tunable white light can be fabricated with phosphors, enabling them for a wider range of applications.

This work describes the observation of lasing in an intermediate chiral phase of a dye-doped cholesteric liquid crystal mixture. This intermediate phase exists between cholesteric and smectic A phase and it presents anomalous selective reflection properties. The lasing was observed at the long-wavelength edge of the photonic band gap.

We present an experimental investigation of a vertical-cavity surface-emitting laser(VCSEL) submitted to orthogonal optical injection, i.e., the injected light is linearly polarized and orthogonal to that emitted by the solitary VCSEL.Bifurcation boundaries of qualitatively different dynamics are mapped out in the frequency detuning-injection strength plane. We unveil rich and complex dynamics including injection locking, limit cycle, wave mixing, and period doubling route to chaos.

A two-element tunable Lyot filter operating in the terahertz (THz) frequency range is demonstrated. The central bandpass frequency of the filter can be continuously tuned from (a fractional tuning range of 40%) using magnetically controlled birefringence in nematic liquid crystals. The transmission bandwidth is and the insertion loss of the present device is due to the scattering of LC molecules in the thick LC cells. This filter can be operated at room temperature.

A negative feedback optical amplification effect was confirmed using negative feedback based on cross-gain modulation in an semiconductor optical amplifier. The optical amplifier with negative feedback was capable of providing an output signal whose gain, wave form and baseline, were stabilized optically. The distortion of the wave form was extremely small in a wide frequency band of . In addition, the gain can be adjusted by controlling the amount of negative feedback power using a variable optical attenuator. In physics, the optical amplifier is considered as the optical equivalent of a noninverting operational amplifier in electronics.

This work presents a photolithographic approach for producing high aspect ratio arrays in photoresist. The photomask is composed of hexagonal/square rod arrays with a thickness of and a period of . Illuminating the photomask with a blue laser generates periodically focused beams up to long and less than wide. A hexagonal rod array provides a better focused beam than a square array due to its higher symmetry. Finite-difference time-domain calculations elucidate the existence of long focused beams above the photomask. Optical near-field measurements verified those subwavelength beams originating from the rod regions.

We generate stable mode-locking of different lateral modes in broad-area semiconductor lasers (BALs) by local injection of short optical pulses repeated at subharmonics of the lateral mode separation. The locking results in a persistent, periodic spatiotemporal dynamics consisting of a laterally alternating intensity modulation with a repetition rate of , which can be regarded as an enhancement and stabilization of the spontaneous dynamic filamentation that is frequently observed in free running BALs.

We report on fast photodetectors operating in the near infrared and realized in pure germanium on silicon. The diodes were fabricated by chemical vapor deposition at without affecting the crystal quality and allowing the integration with standard silicon processes. We demonstrate responsivities of 0.4 and at 1.3 and , respectively, as well as operation at .

We study the enhancement of fluorescence by Ag nanopillars on a semiconducting substrate in which the pillar size, shape, and spacing is varied systematically using electron-beam lithography. Local maxima in the enhancement versus lateral size, as large as a factor of are observed, and vary both with the shape of the pillars and the wavelength of the excitation. We find that the size, shape, and spacing dependence is in qualitative agreement with a model based upon resonant coupling with particle plasmon polaritons. We also find increased enhancement for particle shapes producing high local electric fields.

We have developed a slab laser design based on conduction cooling and a novel pumping geometry called corner pumping. The design uses a slab crystal configuration with the pump light incident from the slab corners. A maximum output power of over was achieved from a thick Yb:YAG/YAG (aluminumgarnet)structure with a -doped Yb:YAG. The slope efficiency and optical-to-optical efficiency with respect to the total pump power were 42.8% and 33.6%, respectively. At this pump power the electrical-to-optical conversion efficiency of the system was 16.8%.

This letter reports on translational velocity measurement, which is needed for tracking a low contrast cell. We propose a new optical spatial filtering method that is based on the optical Fourier transform theory. In this method, a pinhole is installed as a spatial filter on the optical Fourier transform plane. By means of this spatial filter, the arbitrary component of the spatial frequency is derived from the random refractive index distribution as the periodic light intensity distribution. By observing the changes of this light intensity, we can obtain the translational velocity of a low-contrast cell by means of a high-response photodiode.

The plasma electron density in a symmetric confined capacitive-coupled plasma processing tool containing gas mixtures is studied as a function of two, combined radio frequency powers. For measuring we have used a floating hairpin resonance probe. The results show a linear increase in with power. Also the density is higher with an increase in power, in contrast with published particle-in-cell simulation results in argon where the plasma density decreased with increases in low frequency voltage, for fixed high frequency current [P. C. Boyle et al., J. Phys. D37, 697 (2004)]. Analyzing the relative phase between radio frequency current and voltage, we observe slightly lower phase shifts at higher voltage, which is attributed to an increase in the real component of the current through the sheath. This is possible due to the increase in secondary electron emissions arising from ion bombardment, which is favored by an increase in voltage. We therefore conclude that the secondary electrons could play an important role in the discharge process.

Discharge instabilities in x-ray preionized -doped excimer laser gas mixtures are investigated using an intensified charge coupled device camera with a gating time of . In contradiction with earlier theories and observations, it is found that the discharges in mixtures are homogeneous only at very low concentration of (0.025%). We present experimental results, which prove that in mixtures the appearance of discharge filaments is coupled with the presence of rather than Kr.

The anisotropic and plasma screening effects on the electron capture process are investigated in an anisotropicplasma in the presence of an external electric field. The Bohr–Lindhard model with the impact parameter analysis is applied to obtain the electron capture probability in the anisotropicplasma as a function of the impact parameter, Debye length, and collision energy. The result shows that the electron capture cross section decreases with increasing collision energy. It is also found that the anisotropic effect strongly suppresses the electron capture cross section in the anisotropicplasma.

The addition of 3% nitrogen to a mixture of perfluorocarbon/oxygen/argon in a remote toroidal plasma source was shown to double the etching rate of both silicon dioxide and silicon in a downstream process. It is believed that the nitrogen blocks the surface recombination sites for formation on the wall of the transfer tube, thereby transporting more fluorine atoms to the downstream process chamber and increasing the etching rate.

Transparent indiumzinc oxide (IZO) ohmic contacts to phosphor-doped -type ZnO have been formed. The resistance, transmittance, and phase reliability of the contacts were investigated. As deposited, an ohmic contact was formed with a specific contact resistance of about and the transmittance of the film was more than 75% in the wavelength range. After annealing at for in a vacuum , the specific contact resistance was reduced by about two orders of magnitude to , while maintaining the contact stability and high optical transparency.

Chain-like Mg-doped ZnOnanoparticles were prepared using a wet chemical method combined with subsequent heat treatment. The blueshifted near-band-edge emission of the dopedZnO sample with respect to the undoped one was investigated by temperature-dependent photoluminescence. Based on the energy shift of the free-exciton transition, a band gap enlargement of was estimated, which seems to result in the equivalent shift of the bound-exciton transition. At , the transformation from the donor-acceptor-pair to free-to-acceptor emissions was observed for both the undoped and doped samples. The results show that Mgdoping leads to the decrease of the acceptor binding energy.